The invention falls within the field of infrared imaging, corresponding to wavelengths of between 900 nm (nanometers) and 25 μm (micrometers). In this field, photodetectors comprising a photo-absorbent layer made from semiconductor material are used. A photo-absorbent layer is a layer absorbing the photons belonging to a predefined range of wavelengths.
The dark current is one of the main limitations on the performance of a photodetector. The current has a diffusion component in the neutral zones and exacerbated generation-recombination component in the deserted zones. The origin of the dark current includes Shockley-Read generation-recombination, radiative generation-recombination or Auger generation-recombination components with different thermal activation laws.
To improve the performance of the detecting structure, barrier layers are generally superimposed on either side of the absorption layer. A barrier layer is a layer preventing the passage of the majority carriers and allowing the minority carriers to pass. It additionally makes it possible to prevent the formation of a space filler zone and therefore even further limits the dark current.
Such photodetectors comprising a structure with a stack of layers, forming a detection circuit, obtained by epitaxy on a substrate, comprising a barrier layer, for example made from aluminum-gallium arsenide-antimonide (AlGaAsSb), stacked on an absorption layer made from indium arsenide antimonide (InAsSb) on a substrate made from gallium antimonide (GaSb), have an operating temperature of 130 K to 250 K.
The photodetector comprises semi conductor contacts, each contact having an end part in contact with at least one space charge zone. Each contact makes it possible to collect a current formed by the movement of the charge carriers, in the charge zone centered on said contact.
Thus, a photodetection matrix formed by pixels is produced, the pixels each having a length and a width, in general equal and commonly called “pitch of the pixel”.
One known method for producing such a photodetector uses an assembly of indium beads between the photodetection circuit and a reading circuit made from silicon technology intended to collect the current formed by the movement of the charge carriers and convert it into a video signal usable by an image processing chain. The use of indium beads limits the pixel pitch to about 10 μm.
Yet it is desirable for certain applications to decrease the size of the pixel pitch.
Another alternative assembly method is a metallization method known under the name “loop-hole” consisting of producing contacts through the detection circuit. Applied to a structure with a stack of layers as described above, such a method would require placing an etching through the absorption layer, which is an active layer of the stack. This would create a lateral desertion zone in the absence of a barrier along the edge zone, and therefore a strong dark current.
The invention aims to resolve the aforementioned drawbacks, by proposing a method for manufacturing a photodetector with a stack of superimposed layers comprising at least one barrier layer, making it possible to achieve pixel pitches smaller than 10 μm, while limiting the dark current and allowing an operation at temperatures greater than or equal to 150K.